BEIRUT — The Syrian government claimed control of the strategic city of Qusair in central Syria on Wednesday after a nearly three-week fight with rebels who had held the city for a year, a victory for President Bashar Assad that raised questions about what’s next for the Hezbollah fighters considered key to the outcome.

Hezbollah, the Lebanese group that is fighting openly on the side of the Syrian government, tightened security in Beirut’s southern suburbs, its stronghold, in case Syrian rebels carry out threats to attack Hezbollah supporters in Lebanon.

Hezbollah fighters said the group was recruiting more extremists to send to Syria. One Hezbollah official, who asked to be identified only as Hassan, said he would travel soon to Aleppo, Syria’s second-largest city, where government and rebel forces have been in a stalemate for the past 10 months.

Hassan made it clear that religious differences between the Shiite Muslim Hezbollah and the mostly Sunni Muslim rebels in Syria were vital to its ability to find men willing to fight in Syria.

“We’re recruiting,” Hassan said. “The biggest mistake (the rebels) in Syria made is insulting our beliefs. That’s the most dangerous thing you can do.”

How many Hezbollah extremists took part in the fighting for Qusair is unknown, but their intervention on behalf of the Syrian government brought denunciation from rebels and the United States, which called last week for them to withdraw. Hezbollah members interviewed in Beirut portrayed their group as having taken the lead in the fighting, though Assad, in a recorded interview last week with a Hezbollah television station, said the number of Hezbollah fighters was a “drop in the ocean” compared with the number of Syrian government troops fighting the rebels.

There was scant mention of Hezbollah in Syrian news accounts of the fighting. Syrian television broadcast footage of troops in Qusair’s center, largely empty save for their presence. The city appeared heavily damaged, and the pictures were corroborated later by foreign reporters who were allowed to visit the city. They reported that bodies still lay in the street.

There was no official tally of the dead and wounded. Perhaps up to 500 rebels were killed in the government offensive, according to the Reuters news agency, and hundreds more were wounded.

A spokeswoman for the International Committee of the Red Cross (ICRC) and Red Crescent in Damascus, which works with the Syrian Arab Red Crescent to deliver aid, said the group was still waiting for permission from the government to enter Qusair, after being told earlier to wait for an end to the fighting.

The government victory at Qusair complicated plans for a peace conference that the United States and Russia have said they will hold. The opposition coalition had said previously that it wouldn’t attend to protest Hezbollah’s involvement in Qusair, and the U.N.’s Syria envoy, Lakhdar Brahimi, said Wednesday that the talks wouldn’t be until July.